$4r - 4s + t - 9 = -2s + 9t - 2$ Solve for $r$.
Solution: Combine constant terms on the right. $4r - 4s + t - {9} = -2s + 9t - {2}$ $4r - 4s + t = -2s + 9t + {7}$ Combine $t$ terms on the right. $4r - 4s + {t} = -2s + {9t} + 7$ $4r - 4s = -2s + {8t} + 7$ Combine $s$ terms on the right. $4r - {4s} = -{2s} + 8t + 7$ $4r = {2s} + 8t + 7$ Isolate $r$ ${4}r = 2s + 8t + 7$ $r = \dfrac{ 2s + 8t + 7 }{ {4} }$